U.S. patent number 8,449,684 [Application Number 11/783,748] was granted by the patent office on 2013-05-28 for substrate cleaning method, substrate cleaning system and program storage medium.
This patent grant is currently assigned to Tokyo Electron Limited. The grantee listed for this patent is Naoki Shindo, Tsukasa Watanabe. Invention is credited to Naoki Shindo, Tsukasa Watanabe.
United States Patent |
8,449,684 |
Watanabe , et al. |
May 28, 2013 |
Substrate cleaning method, substrate cleaning system and program
storage medium
Abstract
The present invention provides a substrate cleaning method
capable of removing particles from the entire surface of a
substrate to be processed at a high removing efficiency. In the
substrate cleaning method according to the present invention, a
substrate to be processed W is immersed in a cleaning liquid in a
cleaning tank 12. Then, ultrasonic waves are generated in the
cleaning liquid contained in the cleaning tank 12, so that the
substrate W is subjected to an ultrasonic cleaning process. The
step of generating ultrasonic waves includes a step of generating
ultrasonic waves in the cleaning tank while the cleaning liquid is
being supplied into the cleaning tank. A supply rate at which the
cleaning liquid is supplied into the cleaning tank at a certain
timing in the step of generating ultrasonic waves differs from a
supply rate at which the cleaning liquid is supplied into the
cleaning tank at another timing in the step of generating
ultrasonic waves.
Inventors: |
Watanabe; Tsukasa (Nirasaki,
JP), Shindo; Naoki (Nirasaki, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Watanabe; Tsukasa
Shindo; Naoki |
Nirasaki
Nirasaki |
N/A
N/A |
JP
JP |
|
|
Assignee: |
Tokyo Electron Limited (Tokyo,
JP)
|
Family
ID: |
38230031 |
Appl.
No.: |
11/783,748 |
Filed: |
April 11, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070240736 A1 |
Oct 18, 2007 |
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Foreign Application Priority Data
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Apr 13, 2006 [JP] |
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2006-110957 |
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Current U.S.
Class: |
134/18; 134/184;
134/26; 134/1.3; 134/34; 134/902 |
Current CPC
Class: |
B08B
3/12 (20130101); H01L 21/67057 (20130101); B08B
3/048 (20130101) |
Current International
Class: |
B08B
7/00 (20060101); B08B 3/00 (20060101); B08B
7/04 (20060101) |
Field of
Search: |
;134/184,902,1,1.3,34,186,18,26,32 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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8-39025 |
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Feb 1996 |
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JP |
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10-109072 |
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Apr 1998 |
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JP |
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2000-237704 |
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Sep 2000 |
|
JP |
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2004-193329 |
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Jul 2004 |
|
JP |
|
Other References
Japanese Office Action mailed on Oct. 15, 2010 for Japanese
Application No. 2006-110957 with English translation. cited by
applicant.
|
Primary Examiner: Markoff; Alexander
Attorney, Agent or Firm: Smith, Gambrell & Russell,
LLP
Claims
The invention claimed is:
1. A substrate cleaning system comprising: a cleaning tank that
contains a cleaning liquid and accommodates a semiconductor wafer
in an upstanding position therein; an ultrasonic generator that
generates ultrasonic waves in the cleaning liquid contained in the
cleaning tank from below the upstanding semiconductor wafer; a
cleaning liquid supply system that supplies the cleaning liquid
whose dissolved gas concentration is adjusted to a desired
concentration into the cleaning tank; and a control device
configured to control the cleaning liquid supply system and the
ultrasonic generator such that: the control device causes the
cleaning liquid supply system to supply the cleaning liquid into
the cleaning tank at a first supply rate in order to fill the tank
and adjust a dissolved gas concentration in the liquid to a
predetermined value before a semiconductor wafer is immersed in the
cleaning liquid within the tank, after the semiconductor wafer is
immersed in the tank and maintained in the upstanding position, the
control device causes the ultrasonic wave generator to begin
generating ultrasonic waves in the cleaning liquid while causing
the cleaning liquid supply system to reduce, in a stepwise or
stepless manner, the supply rate of the cleaning liquid from the
first supply rate to a second supply rate that is less than the
first supply rate and greater than zero; thereafter, the control
device causes the ultrasonic wave generator to continue generation
of ultrasonic waves in the cleaning liquid while causing the
cleaning liquid supply system to continue supply of the cleaning
liquid at the second supply rate so that cleaning liquid overflows
from the tank through an open upper end of the tank; and
thereafter, the control device causes the ultrasonic wave generator
to continue generation of ultrasonic waves in the cleaning liquid
while causing the cleaning liquid supply system to reduce, in a
stepwise or stepless manner, the supply rate of cleaning liquid
from the second supply rate to a third supply rate that is less
than the second supply rate.
2. The substrate cleaning system according to claim 1, wherein the
third supply rate is zero.
3. A substrate cleaning method comprising the steps of: supplying a
cleaning liquid into a cleaning tank at a first supply rate in
order to fill the tank while adjusting a dissolved gas
concentration in the liquid to a predetermined value; thereafter,
immersing a semiconductor wafer in the cleaning liquid within the
tank and maintaining the wafer upstanding within the tank through
said method; thereafter, beginning generating ultrasonic waves in
the cleaning liquid in the tank from below the wafer while
reducing, in a stepwise or stepless manner, the supply rate of the
cleaning liquid from the first supply rate to a second supply rate
that is less than the first supply rate and greater than zero;
thereafter, continuing generation of ultrasonic waves in the
cleaning liquid while continuing supply of the cleaning liquid at
the second supply rate so that cleaning liquid overflows from the
tank through an open upper end of the tank; and thereafter, while
continuing generation of ultrasonic waves in the cleaning liquid,
reducing, in a stepwise or stepless manner, the supply rate of
cleaning liquid from the second supply rate to a third supply rate
that is less than the second supply rate.
4. The substrate cleaning method according to claim 3, wherein the
third supply rate is zero.
5. A non-transitory storage medium storing a program executed by a
control device for controlling a substrate cleaning system so as to
accomplish the substrate cleaning method according to claim 3.
6. A non-transitory storage medium storing a program executed by a
control device for controlling a substrate cleaning system so as to
accomplish the substrate cleaning method according to claim 4.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority
from the prior Japanese Patent Application No. 2006-110957 filed on
Apr. 13, 2006, the entire contents of which are incorporated herein
by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a substrate cleaning method and a
substrate cleaning system for removing particles (foreign matters)
adhering to a substrate to be processed by immersing the substrate
to be processed in a cleaning liquid and generating ultrasonic
waves in the cleaning liquid. More particularly, the present
invention relates to a substrate cleaning method and a substrate
cleaning system capable of removing particles from the entire
surface of a substrate to be processed at a high removing
efficiency.
The present invention relates also to a program storage medium
storing a program for accomplishing a substrate cleaning method
capable of removing particles from the entire surface of a
substrate to be processed at a high removing efficiency.
2. Description of the Related Art
There is known, from JP10-109072A, for example, a cleaning method,
which cleans a substrate to be processed by immersing the substrate
held by a holding member in a cleaning liquid and by generating
ultrasonic waves in the cleaning liquid. This cleaning method is
generally called an ultrasonic cleaning process, and also called a
megasonic cleaning process. JP10-109072A describes that, in order
to clean a substrate to be processed at a high particle removing
efficiency, it is effective to set a dissolved gas concentration of
a gas dissolved in a cleaning liquid within a predetermined
range.
SUMMARY OF THE INVENTION
Generally, ultrasonic waves are radiated from below a substrate to
be processed. Therefore, there is a possibility that particle
removing efficiency in a part of the substrate is different from
that in another part of the substrate. In particular, because of a
holding member holding the substrate from below which may interfere
with the radiation of the ultrasonic waves, there is a possibility
that some areas in the substrate are cleaned at a lower particle
removing efficiency.
The present invention has been made in view of such a problem and
it is therefore an object of the present invention to provide a
substrate cleaning method and a substrate cleaning system capable
of uniformly removing particles from the surface of a substrate to
be processed at a high removing efficiency. In addition, it is more
preferable that a substrate to be processed is cleaned by the
substrate cleaning method and the substrate cleaning system with a
simple control.
Another object of the present invention is to provide a program
storage medium storing a program for accomplishing a substrate
cleaning method capable of uniformly removing particles from the
entire surface of a substrate to be processed at a high removing
efficiency.
The inventors of the present invention prosecuted extensive studies
regarding how a distribution of a particle removing efficiency of a
single substrate to be processed, which was cleaned in a cleaning
liquid by an ultrasonic cleaning process, differs between a case in
which a cleaning liquid was supplied into a cleaning tank during
when ultrasonic waves were generated in the cleaning liquid
contained in the cleaning tank, and a case in which no cleaning
liquid was supplied into a cleaning tank during when ultrasonic
waves were generated in the cleaning liquid contained in the
cleaning tank. Then, the inventors found that a position of an area
where particles are easily removed changes in the substrate,
depending on whether the cleaning liquid is supplied or not into
the cleaning tank during when ultrasonic waves are generated in the
cleaning liquid contained in the cleaning tank, and depending
further on the increase or decrease in a supply rate of the
cleaning liquid supplied into the cleaning tank during when
ultrasonic waves are generated in the cleaning liquid contained in
the cleaning tank. The present invention is on the basis of this
research.
The substrate cleaning method according to the present invention
comprises the steps of: immersing a substrate in a cleaning liquid
in a cleaning tank; and generating ultrasonic waves in the cleaning
liquid contained in the cleaning tank; wherein the step of
generating ultrasonic waves includes a step of generating
ultrasonic waves in the cleaning liquid contained in the cleaning
tank while the cleaning liquid is being supplied into the cleaning
tank, and a supply rate at which the cleaning liquid is supplied
into the cleaning tank at a certain timing in the step of
generating ultrasonic waves differs from a supply rate at which the
cleaning liquid is supplied into the cleaning tank at another
timing in the step of generating ultrasonic waves.
According to the substrate cleaning method of the present
invention, particles can be uniformly removed from a substrate. At
the same time, a particle removing efficiency can be improved in
the substrate from the overall point of view. In the substrate
cleaning method, the cleaning liquid may be continuously supplied
throughout the period in which ultrasonic waves are generated.
Alternatively, the cleaning liquid may be temporarily supplied
during the period in which ultrasonic waves are generated.
In the substrate cleaning method according to the present
invention, the step of generating ultrasonic waves may further
include a step of generating ultrasonic waves in the cleaning
liquid contained in the cleaning tank while the supply of the
cleaning liquid is stopped. In the step of generating ultrasonic
waves, the step of generating ultrasonic waves in the cleaning
liquid contained in the cleaning tank while the cleaning liquid is
being supplied into the cleaning tank, and the step of generating
ultrasonic waves in the cleaning liquid contained in the cleaning
tank while the supply of the cleaning liquid is stopped may be
carried out once or more times, respectively.
In the step of generating ultrasonic waves in the cleaning liquid
contained in the cleaning tank while the cleaning liquid is being
supplied into the cleaning tank, a supply rate at which the
cleaning liquid is supplied into the cleaning tank may be changed
in a stepwise manner or stepless manner. According to the substrate
cleaning method of the present invention, particles can be more
uniformly removed from a substrate. At the same time, a particle
removing efficiency can be more improved in the substrate from the
overall point of view. Alternatively, in the step of generating
ultrasonic waves in the cleaning liquid contained in the cleaning
tank while the cleaning liquid is being supplied into the cleaning
tank, a supply rate at which the cleaning liquid is supplied into
the cleaning tank may be maintained constant.
Further, the step of generating ultrasonic waves in the cleaning
liquid contained in the cleaning tank while the supply of the
cleaning liquid is stopped may be carried out after the step of
generating ultrasonic waves in the cleaning liquid contained in the
cleaning tank while the cleaning liquid is being supplied into the
cleaning tank.
Further, in the step of generating ultrasonic waves, a supply rate
at which the cleaning liquid is supplied into the cleaning tank may
be changed in a stepwise manner or stepless manner.
A substrate cleaning system according to the present invention
comprises: a cleaning tank that contains a cleaning liquid; an
ultrasonic generator that generates ultrasonic waves in the
cleaning liquid contained in the cleaning tank; a cleaning liquid
supply system that supplies the cleaning liquid into the cleaning
tank; and a control device that controls the supply of the cleaning
liquid by the cleaning liquid supply system and the generation of
ultrasonic waves by the ultrasonic generator in the cleaning liquid
contained in the cleaning tank; wherein the control device controls
the supply of the cleaning liquid and the generation of ultrasonic
waves in such a manner that: the cleaning liquid is supplied into
the cleaning tank for at least a certain period of time during when
ultrasonic waves are generated in the cleaning liquid contained in
the cleaning tank; and that a supply rate at which the cleaning
liquid is supplied into the cleaning tank at a certain timing
during when ultrasonic waves are generated in the cleaning liquid
contained in the cleaning tank differs from a supply rate at which
the cleaning liquid is supplied into the cleaning tank at another
timing during when ultrasonic waves are generated in the cleaning
liquid contained in the cleaning tank.
According to the substrate cleaning system of the present
invention, particles can be uniformly removed from a substrate. In
addition, a particle removing efficiency can be improved in the
substrate from the overall point of view. In the substrate cleaning
system, the cleaning liquid may be continuously supplied throughout
the period in which ultrasonic waves are generated. Alternatively,
the cleaning liquid may be temporarily supplied during the period
in which ultrasonic waves are generated.
In the substrate cleaning system according to the present
invention, the control device may control the supply of the
cleaning liquid and the generation of ultrasonic waves in such a
manner that the supply of the cleaning liquid into the cleaning
tank is stopped for another period of time other than the certain
period of time during when ultrasonic waves are generated in the
cleaning liquid contained in the cleaning tank. During when
ultrasonic waves are generated, there may be one or more period(s)
of time in which the cleaning liquid is supplied into the cleaning
tank, and one or more period(s) of time in which the supply of the
cleaning liquid into the cleaning tank is stopped.
In the substrate cleaning system, in the certain period of time in
which the cleaning liquid is supplied into the cleaning tank, the
control device may control the supply of the cleaning liquid and
the generation of ultrasonic waves in such a manner that a supply
rate at which the cleaning liquid is supplied into the cleaning
tank is changed in a stepwise manner or stepless manner. According
to the substrate cleaning system of the present invention,
particles can be more uniformly removed from a substrate. At the
same time, a particle removing efficiency can be more improved in
the substrate from the overall point of view. Alternatively, in the
substrate cleaning system, in the certain period of time in which
the cleaning liquid is supplied into the cleaning tank, the control
device may control the supply of the cleaning liquid and the
generation of ultrasonic waves in such a manner that a supply rate
at which the cleaning liquid is supplied into the cleaning tank is
maintained constant.
Further, in the substrate cleaning system, during when ultrasonic
waves are generated, the control device may control the supply of
the cleaning liquid and the generation of ultrasonic waves in such
a manner that the cleaning liquid is supplied into the cleaning
tank at first, and then the supply of the cleaning liquid into the
cleaning tank is stopped.
Further, in the substrate cleaning system, during when ultrasonic
waves are generated, the control device may control the supply of
the cleaning liquid and the generation of ultrasonic waves in such
a manner that a supply rate at which the cleaning liquid is
supplied into the cleaning tank is changed in a stepwise manner or
stepless manner.
A program storage medium according to the present invention is a
storage medium storing a program executed by a control device for
controlling a substrate cleaning system so as to accomplish a
substrate cleaning method comprising the steps of: immersing a
substrate in a cleaning liquid in a cleaning tank; and generating
ultrasonic waves in the cleaning liquid contained in the cleaning
tank; wherein the step of generating ultrasonic waves includes a
step of generating ultrasonic waves in the cleaning liquid
contained in the cleaning tank while the cleaning liquid is being
supplied into the cleaning tank, and a supply rate at which the
cleaning liquid is supplied into the cleaning tank at a certain
timing in the step of generating ultrasonic waves differs from a
supply rate at which the cleaning liquid is supplied into the
cleaning tank at another timing in the step of generating
ultrasonic waves.
A program according to the present invention is a program executed
by a control device for controlling a substrate cleaning system so
as to accomplish a substrate cleaning method comprising the steps
of: immersing a substrate in a cleaning liquid in a cleaning tank;
and generating ultrasonic waves in the cleaning liquid contained in
the cleaning tank; wherein the step of generating ultrasonic waves
includes a step of generating ultrasonic waves in the cleaning
liquid contained in the cleaning tank while the cleaning liquid is
being supplied into the cleaning tank, and a supply rate at which
the cleaning liquid is supplied into the cleaning tank at a certain
timing in the step of generating ultrasonic waves differs from a
supply rate at which the cleaning liquid is supplied into the
cleaning tank at another timing in the step of generating
ultrasonic waves.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view showing a schematic structure of a substrate
cleaning system in one embodiment of the present invention;
FIG. 2 is a cross-sectional view taken on the line II-II in FIG.
1;
FIG. 3 is a diagram for explaining a change in a supply rate at
which a cleaning liquid is supplied from a cleaning liquid supply
system in connection with an operating mode of an ultrasonic
generator;
FIG. 4 is a view for explaining a mode of propagation of ultrasonic
waves in the cleaning liquid;
FIG. 5 is a view for explaining a mode of propagation of ultrasonic
waves in the cleaning liquid;
FIG. 6 is a diagram corresponding to FIG. 3, for explaining an
alternative example of a change in a supply rate at which the
cleaning liquid is supplied from the cleaning liquid supply system
in connection with an operating mode of the ultrasonic generator;
and
FIG. 7 is a view for explaining a relation between the supply of
the cleaning liquid or lack thereof from the cleaning liquid supply
system, and an area with a high particle removing efficiency in a
wafer.
DESCRIPTION OF THE PREFERRED EMBODIMENT
A preferred embodiment of the present invention will be described
with reference to the accompanying drawings. In the below
embodiment, a substrate cleaning system according to the present
invention will be described as applied to a semiconductor wafer
cleaning system. However, the present inventions is not limited to
the semiconductor wafer cleaning system, and can be applied widely
to substrate cleaning systems.
FIGS. 1 to 5 are views showing a substrate cleaning method, a
substrate cleaning system, a program, and a storage medium in this
embodiment of the present invention.
FIG. 1 is a view showing a schematic structure of the substrate
cleaning system. FIG. 2 is a cross-sectional view taken on the line
II-II in FIG. 1. FIG. 3 is a diagram for explaining an operating
mode of an ultrasonic generator and a change in a supply rate of a
cleaning liquid supplied from a cleaning liquid supply system.
FIGS. 4 and 5 are views for explaining a mode of propagation of
ultrasonic waves in the cleaning liquid.
Referring to FIG. 1, a substrate cleaning system 10 in this
embodiment of the present invention includes: a cleaning tank (DIP
tank) 12; a cleaning liquid supply system 40 connected to the
cleaning tank 12 so as to supply a cleaning liquid into the
cleaning tank 12; a holding member (also referred to as "wafer
boat") 20 for holding wafers to be processed (substrates to be
processed) W, an ultrasonic generator 30 for generating ultrasonic
waves in the cleaning liquid contained in the cleaning tank 12; and
a control device 18 connected to the cleaning liquid supply system
40 and the ultrasonic generator 30. The substrate cleaning system
10 immerses wafers to be processed W in the cleaning liquid
contained in the cleaning tank 12 and generates ultrasonic waves in
the cleaning liquid so as to clean the wafers to be processed W by
ultrasonic cleaning.
The cleaning liquid supply system 40 is described in detail at
first. As shown in FIG. 1, the cleaning liquid supply system 40
includes: a pump 42 that delivers a cleaning liquid in which a gas,
such as an air, preferably an inert gas, and more preferably
nitrogen, is dissolved; and a connecting pipe 50 that connects the
pump 42 and the cleaning tank 12 to each other. In this embodiment,
the pump 42 is connected to a pure water source, not shown, so as
to deliver, as a cleaning liquid, a pure water (e.g., deionized
water (DIW)) stored in the pure water source into the connecting
pipe 50. The pump may be, e.g., an air-driven bellows pump which is
capable of adjusting a delivering rate by adjusting an air
pressure. As shown in FIG. 1, the connecting pipe 50 is provided
with an on-off valve 54, so that the connecting pipe 50 can be
opened and/or closed by means of the on-off valve 54.
As shown in FIG. 1, the cleaning liquid supply system 40 also
includes a chemical supply unit 47 for supplying a chemical element
to a pure water flowing through the connecting pipe 50. The
chemical supply unit 47 has: a first mixing valve 55 placed in the
connecting pipe 50; and a first chemical source 48 and a second
chemical source 49 that are connected to the first mixing valve 55
so as to supply chemical elements thereto. In this embodiment, the
first chemical source 48 supplies hydrogen peroxide as a first
chemical element, and the second chemical source 49 supplies
ammonia as a second chemical element. Thus, by supplying hydrogen
peroxide and ammonia from the first chemical source 48 and the
second chemical source 49, respectively, into the connecting pipe
50, and mixing the hydrogen peroxide and the ammonia with the pure
water in the connecting pipe 50, a chemical solution, namely, an
ammonia-hydrogen peroxide solution SC1
(NH.sub.4OH/H.sub.2O.sub.2/H.sub.2O) can be supplied into the
supply tank 12.
As shown in FIGS. 1 and 2, two cleaning nozzles 56, which extend
along opposed wall surfaces of the cleaning tank 12, are connected
to ends of the connecting pipe 50 on a side of the cleaning tank
12. The cleaning nozzles 56 are elongated tubular members extending
along the wall surfaces of the cleaning tank 12. The tubular member
is provided with a number of nozzle holes 56a which are arranged at
fixed longitudinal intervals. The positions of the nozzle holes 56a
are dependent on the positions of the wafers to be processed W held
by the holding member 20, which is described hereinbelow.
As described above, the control device 18 connected to the cleaning
liquid supply system 40 controls the cleaning liquid supply system
40. More concretely, the control device 18 starts and stops the
pump 42, and controls a delivering rate at which the cleaning
liquid is delivered by the pump 42 while it is driven for
operation, and a supply of the chemical element from the chemical
supply unit 47. When the pump 42 is an air-driven bellows pump, a
delivering rate of the air-driven bellows pump, namely, the pump 42
can be controlled by controlling an air pressure applied to the
air-driven bellows pump. When the pump 42 is a pumping device other
than an air-driven bellows pump, such as an electric pump, a
delivering rate of the pump 42 can be controlled by controlling a
power supplied to the electric pump.
As shown by the two-dot chain lines in FIG. 1, a deaerator 43, a
dissolving device 44, a temperature adjusting device 45, and so on
may be placed in the connecting pipe 50 according to need.
The deaerator 43 is a device for removing dissolved gases from the
cleaning liquid flowing through the connecting pipe 50. The
deaerator 43 may be any suitable one of known membrane deaerators
and vacuum deaerators. The relation between the input to the
deaerator 68 and the amount of gases corresponding to the input
that can be removed from the cleaning liquid, namely, the reduction
of the dissolved gas concentration corresponding to the input, is
determined beforehand. An input to the deaerator 43 is determined
according to a desired amount of gases to be removed on the basis
of the thus determined relation and the determined input is
supplied to the deaerator 43. Thus, a cleaning liquid in which a
gas is dissolved at a desired dissolved gas concentration can be
obtained.
The dissolving device 44 connected to a gas source 44a is a device
for dissolving a gas supplied from the gas source 44a in the
cleaning liquid flowing through the connecting pipe 50. Similar to
the deaerator 43, the dissolving device 44 may be any suitable one
of various known dissolving devices. The relation between the input
to the dissolving device 44 and the amount of gases corresponding
to the input that can be dissolved in the cleaning liquid, namely,
the increase of the dissolved gas concentration corresponding to
the input, is determined beforehand. An input to the dissolving
device 44 is determined according to a desired amount of gases to
be dissolved on the basis of the thus determined relation and the
determined input is supplied to the dissolving device 44. Thus, a
cleaning liquid in which a desired gas stored in the gas source 44a
is dissolved at a desired dissolved gas concentration can be
obtained.
Further, as shown in FIG. 1, it is preferable to dispose both the
deaerator 43 and the dissolving device 44 such that the deaerator
43 is positioned on an upstream side of the dissolving device 44.
In this case, a cleaning liquid in which only a desired gas such as
nitrogen supplied from the gas source 44a is dissolved at a desired
dissolved gas concentration can be obtained by making at first the
dissolved gas concentration of the cleaning liquid in the
connecting pipe 50 be 0% by the deaerator 43, and then adjusting
the dissolved gas concentration to the desired one by the
dissolving device 44.
The temperature adjusting device 45 heats and/or cools the
connecting pipe 50 so as to adjust the temperature of the cleaning
liquid flowing through the connecting pipe 50. The temperature
adjusting device 45 may be a known heating device or a known
cooling device.
The cleaning tank 12 into which the cleaning liquid is supplied by
the cleaning liquid supply system 40 is described. As shown in
FIGS. 1 and 2, the cleaning tank 12 has an a shape substantially
resembling a rectangular solid. The cleaning tank 12 has an open
upper end through which wafers W are carried into and carried out
of the cleaning tank 12, which will be described hereinafter. A
drain pipe 13 is connected to a bottom wall of the cleaning tank 12
so as to drain the cleaning liquid from the cleaning tank 12.
As shown in FIG. 1, an outer tank (recovery tank) 15 surrounds the
open upper end of the cleaning tank 12. The cleaning liquid
overflowing from the cleaning tank 12 through the open upper end is
received in the outer tank 15. Similar to the cleaning tank 12, a
drain pipe 16 is connected to the outer tank 15 so as to drain the
cleaning liquid from the outer tank 15.
The cleaning tank 12 and the outer tank 15 are made of a material
having a high chemical resistance, such as quartz or the like. The
cleaning liquid drained through the drain pipes 13 and 16 of the
respective cleaning tanks 12 and the outer tank 15 may be
discarded, or resupplied into the cleaning tank 12 through a filter
or the like.
The holding member 20 for holding the wafers W is described.
Referring to FIGS. 1 and 2, the holding member 20 has four support
bars 22 extending substantially along a horizontal direction, and a
base 24 holding the four support bars 22 in a cantilever fashion. A
plurality of wafers W, which are to be cleaned at the same time,
namely, a batch formed of, e.g., fifty wafers W is supported on the
support bars 22 from below. The support bars 22 are provided with
grooves, not shown, longitudinally arranged at fixed intervals. The
surfaces of the wafers W engaged in the grooves of the support bars
22 are substantially perpendicular to a direction in which the
support bars 22 are extended. That is to say, the wafers W are
supported on the holding member 20 with the surfaces thereof
extended vertically as shown in FIG. 1.
As obvious from FIG. 2, pitches of the nozzle holes 56a of the
cleaning nozzles 56 are substantially equal to pitches of the
wafers W supported on the holding member 20. The nozzle holes 56a
of the cleaning nozzles 56 are arranged so as to supply the
cleaning liquid into spaces between the adjacent wafers W held by
the holding member 20.
The base 24 of the holding member 20 is connected to a lifting
mechanism, not shown. The lifting mechanism lowers the holding
member 20 supporting the wafers W so as to immerse the wafers W in
the cleaning liquid contained in the cleaning tank 12. The lifting
mechanism is connected to the control device 18. Thus, the control
device 18 controls the lifting mechanism so as to immerse the
wafers W in the cleaning liquid.
The ultrasonic generator 30 is described. As shown in FIG. 1, the
ultrasonic generator 30 includes: vibrating members 38 attached to
the outer surface of the bottom wall of the cleaning tank 12; a
high-frequency power source 32 for driving the vibrating members
38; and an ultrasonic oscillator 34 connected to the high-frequency
power source 32. In this embodiment, each of the vibrating members
38 covers a part of the outer surface of the bottom wall of the
cleaning tank 12. As shown in FIG. 1, the ultrasonic generator 30
further includes a driving mode selector 36 connected to the
ultrasonic oscillator 34 and the vibrating members 38. The driving
mode selector 36 selects a total driving mode in which all the
vibrating members 38 are driven for ultrasonic wave generation, or
a partial driving mode in which one or some of the vibrating
members 38 are driven individually for ultrasonic wave
generation.
The vibrating members 38 are driven for vibration. Then, ultrasonic
waves are transmitted through the bottom wall of the cleaning tank
12 to the cleaning liquid contained therein. Thus, the ultrasonic
waves are propagated in the cleaning liquid contained in the
cleaning tank 12. The ultrasonic generator 30 is connected to the
control device 18. Thus, the control device 18 controls the
radiation (application) of the ultrasonic waves to the cleaning
liquid.
The control device 18 is described. As mentioned above, the control
device 18 is connected to the components of the substrate cleaning
system 10 so as to control operations of these components. In this
embodiment, the control device 18 includes a computer. The computer
executes a program stored beforehand in a storage medium 19 so as
to accomplish a wafer cleaning method by the substrate cleaning
system 10.
A cleaning method for a wafer W to be carried out by the substrate
cleaning system 10 as structured above will be described by way of
example with reference to FIGS. 3 to 5.
In accordance with signals provided by the control device 18, the
pump 42 is driven for delivering a pure water as a cleaning liquid
into the connecting pipe 50. Meanwhile, the first chemical source
48 and the second chemical source 49 of the chemical supply unit 47
supply hydrogen peroxide and ammonia, respectively, into the
connecting pipe 50. Thus, a chemical solution SC1 as a cleaning
liquid of, e.g., 25.degree. C. is supplied into the cleaning tank
12 through the cleaning nozzles 56 of the chemical liquid supply
system 40.
In this supplying step, the control device 18 controls the cleaning
liquid supply system 40 according to a predetermined program such
that a supply rate at which the cleaning liquid is supplied into
the cleaning tank 12 is maintained constant at, e.g., a
predetermined rate A (l/min) as shown in FIG. 3, for example. The
control device 18 controls supply rates of the chemical elements
supplied from the respective chemical sources 48 and 49 into the
connecting pipe 50 based on the supply rate of the cleaning liquid
(pure water) flowing through the connecting pipe 50.
When the deaerator 43 and the dissolving device 44 are placed in
the connecting pipe 50 as shown by the two-dot chain lines in FIG.
1, the control device 18 controls the deaerator 43 and the
dissolving device 44 according to a predetermined program such that
a dissolved gas concentration of the cleaning liquid supplied from
the cleaning liquid supply system 40 into the cleaning tank 12
takes a predetermined value.
According to the above steps, the cleaning tank 12 is filled with
the cleaning liquid (SC1) after a time point a shown in FIG. 3.
The control device 18 drives the lifting mechanism, not shown,
connected to the wafer holding member 20 holding, for example,
fifty wafers W so as to move the wafer holding member 20 downward
and so as to immerse the wafers W in the cleaning liquid contained
in the cleaning tank 12.
Then, the control device 18 actuates the ultrasonic generator 30 so
as to generate ultrasonic waves in the cleaning liquid contained in
the cleaning tank 12. Thus, the wafers W immersed in the cleaning
liquid contained in the cleaning tank 12 are subjected to an
ultrasonic cleaning process (megasonic process) so as to remove
particles (foreign matters) adhering to the surfaces of the wafers
W.
In this embodiment, as shown in FIG. 3, the cleaning liquid
(chemical liquid) is continuously supplied (replenished) from the
connecting pipe 50 of the cleaning liquid supply system 40 into the
cleaning tank 12 such that the cleaning liquid is partially
replaced with the replenished cleaning liquid. However, in this
cleaning step, the control device 18 controls the cleaning liquid
supply system 40 according to a predetermined program such that a
supply rate at which the cleaning liquid is supplied into the
cleaning tank 12 is maintained constant at, e.g., a predetermined
rate B (l/min) as shown in FIG. 3. As shown in FIGS. 1 and 2, the
cleaning liquid is jetted diagonally upward toward a space between
the adjacent two wafers held by the holding member 20. By keeping
the supply of the cleaning liquid into the cleaning tank 12, the
cleaning liquid overflows from the cleaning tank 12. The cleaning
liquid overflowing from the cleaning tank 12 is received in the
outer tank 15.
The above-described first ultrasonic cleaning step in which
ultrasonic waves are generated in the cleaning liquid contained in
the cleaning tank 12 while the cleaning liquid is being supplied by
the cleaning liquid supply system 40 continues for 5 minutes, for
example, which is the term between the time point a and the time
point b shown in FIG. 3.
Thereafter, in this embodiment, while the radiation of ultrasonic
waves by the ultrasonic generator 30 is continued, the supply of
the cleaning liquid by the cleaning liquid supply system 40 is
stopped. This second ultrasonic cleaning step, in which ultrasonic
waves are generated by the ultrasonic generator 30 in the cleaning
liquid contained in the cleaning tank 12 while the supply of the
cleaning liquid by the cleaning liquid supply system 40 is
suspended, continues for 5 minutes, for example, which is the term
between the time point b and the time point c shown in FIG. 3.
That is to say, the substrate cleaning method in this embodiment
includes the first ultrasonic cleaning step in which the ultrasonic
cleaning is conducted while the cleaning liquid is being
replenished into the cleaning tank 12, and the second ultrasonic
cleaning step in which the ultrasonic cleaning is conducted while
the replenishment of the cleaning liquid into the cleaning tank 12
is suspended. As apparent from the examples hereinbelow, a position
of an area where particles are easily removed changes in the wafer
W, depending on the supply of the cleaning liquid or lack thereof
into the cleaning tank during when the ultrasonic waves are
generated in the cleaning liquid contained in the cleaning tank. In
other words, according to this embodiment, it is possible to clean,
in the second ultrasonic cleaning step, a portion of the wafer from
which particles are difficult to be removed in the first ultrasonic
cleaning step. As a result, particles can be more uniformly removed
from the wafer W, and a particle removing efficiency can be
improved in the wafer W from the overall point of view.
Although a mechanism of this phenomenon is not clearly known, a
mechanism that can be one of the factors will be described with
reference to FIGS. 4 and 5. However, the present invention is not
limited to the mechanism described below.
In ultrasonic cleaning, ultrasonic waves propagated in the cleaning
liquid generate pressure vibrations in the cleaning liquid. Gas
molecules contained in the cleaning liquid are ruptured by the
pressure variation (pressure vibrations). The rupture of the gas
molecules generates shock waves (cavitation). It is inferred that
the generation of the shock waves (cavitation) is one of major
factors that peels (removes) particles from the wafers W. Thus, it
is assumed that the higher the dissolved gas concentration of the
cleaning liquid, the higher the intensity of the shock waves
generated in regions in which ultrasonic waves are propagated and
that the shock waves of a high intensity can remove particles from
the wafers W at a high removing efficiency. On the other hand, as
mentioned in JP10-109072A, it is thought that, when the dissolved
gas concentration of the cleaning liquid is high, the gas dissolved
in the cleaning liquid absorbs the ultrasonic waves, which may
interfere with pervasion of the ultrasonic waves throughout the
cleaning tank 12.
Gas molecules dissolved in the cleaning liquid tend to gather in
regions where negative pressures are produced by ultrasonic waves.
Thus, bubbles are produced in these regions, and these bubbles
gradually grow large and eventually rise to the surface of the
cleaning liquid. Therefore, it is assumed that the dissolved gas
concentration of the cleaning liquid decreases if ultrasonic waves
are continuously generated without supplying (replenishing) a new
cleaning liquid into the cleaning tank 12. The production and
growth of bubbles are promoted particularly in a lower part of the
cleaning liquid contained in the cleaning tank 12 where intense
pressure vibrations occur and from which bubbles start moving. As a
result, the dissolved gas concentration of the cleaning liquid
decreases from the lower part in the cleaning tank. On the other
hand, since the outside air can be dissolved in the cleaning liquid
near the surface thereof, the dissolved gas concentration in the
upper part of the cleaning tank 12 is resistant to decrease, or
rather may be maintained near at a saturated concentration.
In view of the above, it is assumed that, as shown in FIG. 4, in
the first ultrasonic cleaning step in which the ultrasonic cleaning
is conducted while the cleaning liquid is being replenished into
the cleaning tank 12, it is expected that particles on a lower area
of the wafer W can be removed at a high removing efficiency, since
the lower area of the wafer W is exposed to the lower part of the
cleaning liquid where the pressure largely varies. It is also
assumed that, a particle removing efficiency is degraded in areas
of the wafer positioned above the support bars 22 which interfere
with the ultrasonic waves radiated from below.
On the other hand, in the second ultrasonic cleaning step in which
the ultrasonic cleaning is conducted while the replenishment of the
cleaning liquid into the cleaning tank 12 is suspended, it is
assumed that the dissolved gas concentration of the cleaning liquid
in the lower part of the cleaning tank 12 decreases as time passes.
Meanwhile, it is assumed that the dissolved gas concentration of
the cleaning liquid in the upper part of the cleaning tank 12 is
maintained higher than at least the dissolved gas concentration of
the cleaning liquid in the lower part of the cleaning tank 12. As a
result, as shown in FIG. 5, it is assumed that ultrasonic waves are
propagated up to the surface of the cleaning liquid without being
greatly absorbed by the dissolved gas in the lower part of the
cleaning tank 12, and then reflected by the surface so as to be
diffused in the cleaning tank 12. Thus, it is expected that
particles on the upper area of the wafer W can be removed at a high
removing efficiency, since the dissolved gas concentration of the
cleaning liquid in the upper part of the cleaning tank 12 can be
maintained relatively high.
In short, according to this embodiment, since the first ultrasonic
cleaning step in which the ultrasonic cleaning is conducted while
the cleaning liquid is being replenished into the cleaning tank 12
is carried out at first, and then the second ultrasonic cleaning
step in which the ultrasonic cleaning is conducted while the
replenishment of the cleaning liquid into the cleaning tank 12 is
suspended is carried out. Thus, in the first ultrasonic cleaning
step, particles on the lower area in the wafer W can be mainly
removed at a high removing efficiency. Then, in the second
ultrasonic cleaning step, particles on the upper area in the wafer
W can be mainly removed at a high removing efficiency. Thus,
particles can be relatively uniformly removed from the entire
surface of the wafer W, and particles can be removed from the wafer
W at relatively a high removing efficiency.
At the time point c shown in FIG. 3, the control device 18 provides
signals to stop the radiation of ultrasonic waves by the ultrasonic
generator 30 so as to finish the second ultrasonic cleaning step in
which the ultrasonic cleaning is conducted while the replenishment
of the cleaning liquid into the cleaning tank 12 is suspended.
After the second ultrasonic cleaning step is finished, there
succeeds a rinsing step for rinsing off the chemical solution as a
cleaning liquid from the wafer. Specifically, the cleaning liquid
(chemical solution) in the cleaning tank 12 and the cleaning liquid
(chemical solution) in the outer tank 15 are drained through the
respective drain pipes 13 and 16. As described above, the drained
cleaning liquid may be discarded or collected for reuse. Then, a
cleaning liquid is supplied again from the connecting pipe 50. Note
that, in this step, no chemical element is supplied from the first
chemical source 48 and the second chemical source 49 of the
chemical supply unit 47 into the connecting pipe 50. Thus, the
cleaning liquid supplied into the cleaning tank 12 is a pure
water.
In this rinsing step, after the cleaning tank 12 is filled with the
cleaning liquid (pure water) as described above, the cleaning
liquid (pure water) is still supplied from the connecting pipe 50.
The cleaning liquid (pure water) overflows from the open upper end
of the cleaning tank 12, and the cleaning liquid (pure water) that
overflowed is received in the outer tank 15. The rinsing step of
the wafers W is thus performed. The cleaning liquid (pure water)
received in the outer tank 15 may be discarded or reused.
When the rinsing step of the wafers W is finished, the holding
member 20 moves upward so as to unload the wafers from the cleaning
tank 12. Thus, a series of cleaning steps for cleaning the wafers W
is completed.
In the above-described embodiment, the first ultrasonic cleaning
step in which the ultrasonic cleaning is conducted while the
cleaning liquid is being replenished into the cleaning tank 12 so
as to replace the cleaning liquid contained in the cleaning tank 12
with new one is performed at first, and then the second ultrasonic
cleaning step in which the ultrasonic cleaning is conducted while
the replenishment of the cleaning liquid into the cleaning tank 12
is suspended is performed. That is to say, the wafer W is subjected
to the ultrasonic cleaning process in which the dissolved gas
concentration distribution of the cleaning liquid in contact with
the surface of the wafer W differs between the first ultrasonic
cleaning step and the second ultrasonic cleaning step. With this
variation in the dissolved gas concentration distribution of the
cleaning liquid in contact with the surface of the wafer W, a
position of an area where particles are easily removed changes in
the wafer W. Thus, it is possible to more uniformly remove
particles from the wafer W. Further, the particle removing
efficiency in the wafer W can be enhanced on the whole. In
addition, this cleaning method can be realized by changing the
control method of the existing substrate cleaning system 10.
Therefore, costs required for the system capable of realizing this
cleaning method can be reduced, which leads to a reduction in costs
required for cleaning the wafer W.
The above embodiment can be modified in various ways within the
scope of the present invention. Modifications of the present
invention will be described below by way of example.
In the foregoing embodiment, the ultrasonic cleaning is conducted
while the cleaning liquid is being replenished into the cleaning
tank 12, and then the ultrasonic cleaning is conducted while the
replenishment of the cleaning liquid into the cleaning tank 12 is
suspended. However, the present invention is not limited thereto.
As a modification, it is possible to conduct the ultrasonic
cleaning while the replenishment of the cleaning liquid into the
cleaning tank 12 is suspended, and then conduct the ultrasonic
cleaning while the cleaning liquid is being replenished into the
cleaning tank 12. Namely, the order of the first ultrasonic
cleaning step and the second ultrasonic cleaning step in the
above-described embodiment may be reversed.
In view of the fact that a position of an area where particles are
easily removed changes in the wafer W depending on the supply of
the cleaning liquid or lack thereof into the cleaning tank 12
during the ultrasonic cleaning, as well as the above-described
assumed mechanism and the below-described experiment results
compatible with this mechanism, it can be understood that a
position of an area where particles are easily removed changes in a
substrate, depending not only on the supply of the cleaning liquid
or lack thereof, but also on the increase or decrease in a supply
rate at which the cleaning liquid is supplied into the cleaning
tank 12 during the ultrasonic cleaning. Various modifications are
possible based on this understanding. FIG. 6 shows such
modifications by way of example. FIG. 6 is a diagram corresponding
to FIG. 3, for explaining a change in a supply rate at which the
cleaning liquid is supplied from the cleaning liquid supply system
40 in relation to an operating mode of the ultrasonic generator
30.
In Modification 1 shown in FIG. 6, a supply rate at which the
cleaning liquid is supplied from the cleaning liquid supply system
40 into the cleaning tank 12 is maintained at a supply rate B1
(l/min) between the time point a1 and the time point d1, and is
then maintained at a supply rate C1 (l/min) between the time point
d1 and the time point e1. Thereafter, the supply of the cleaning
liquid is stopped. Namely, in Modification 1, the supply rate at
which the cleaning liquid is supplied into the cleaning tank 12 is
changed twice in a stepwise manner, i.e., from the first stage to
the second stage and then from the second stage to the third stage,
during when ultrasonic waves are generated in the cleaning liquid
contained in the cleaning tank 12.
In Modification 2 shown in FIG. 6, a supply rate at which the
cleaning is supplied from the cleaning liquid supply system 40 into
the cleaning tank 12 is maintained at a supply rate B2 (l/min)
between the time point a1 and the time point b2, and is then
maintained at a supply rate C2 (l/min) between the time point b2
and the time point c1. Namely, in Modification 2, the cleaning
liquid is continuously supplied into the cleaning tank 12, during
when ultrasonic waves are generated in the cleaning liquid
contained in the cleaning tank 12. The supply rate at which the
cleaning liquid is supplied into the cleaning tank 12 is changed in
the course of the ultrasonic cleaning.
In Modification 3 shown in FIG. 6, at the time point a1, the
ultrasonic generator 30 starts, and simultaneously the cleaning
liquid supply system 40 supplies the cleaning liquid into the
cleaning tank 12 at a supply rate B3 (l/min). Then, the supply rate
at which the cleaning liquid is supplied into the cleaning tank 12
is gradually decreased in a stepless manner as time passes. At the
time point c1, the ultrasonic generator 30 stops, and
simultaneously the supply of the cleaning liquid into the cleaning
tank 12 is stopped.
In Modification 4 shown in FIG. 6, between the time point a1 and
the time point c1 in which the ultrasonic generator 30 is in
operation, the cleaning liquid supply system 40 continues to supply
the cleaning liquid into the cleaning tank 12. In Modification 4, a
supply rate at which the cleaning liquid is supplied into the
cleaning tank 12 is changed as time passes between not more than a
supply rate B4 (l/min) and not less than a supply rate C4
(l/min).
As can be seen from Modifications 1 to 4 shown in FIG. 6, the
cleaning liquid supply system 40 may continue to supply the
cleaning liquid into the cleaning tank 12 during the operation of
the ultrasonic generator 30 (Modifications 2 to 4), or the cleaning
liquid supply system 40 may suspend the supply of the cleaning
liquid into the cleaning tank 12 for a certain period of time
during the operation of the ultrasonic generator 30 (Modification
1). Further, a supply rate at which the cleaning liquid is supplied
by the cleaning liquid supply system 40 into the cleaning tank 12
may either be changed in a stepwise manner (Modification 1 and
Modification 2) or stepless manner (Modification 3 and Modification
4). Furthermore, the stepwise manner and the stepless manner may be
suitably combined. In the stepwise manner, a supply rate at which
the cleaning liquid is supplied may be changed twice or more times.
In addition, the step in which the ultrasonic cleaning is conducted
while the cleaning liquid is being supplied, and the step in which
the ultrasonic cleaning is conducted while the supply of the
cleaning liquid into the cleaning tank is suspended may be
repeated.
In the foregoing embodiment, a supply rate at which the cleaning
liquid is supplied by the cleaning liquid supply system 40 into the
cleaning tank 12 is changed by changing a delivering rate of the
pump 42. However, the present invention is not limited thereto, and
various known methods can be adopted. For example, a supply rate
may be changed by changing an opening degree of a valve placed in
the connecting pipe 50.
In the foregoing embodiment, SC1 is used as a cleaning liquid for
the ultrasonic cleaning of the wafers W. However, not limited
thereto, the wafers W may be cleaned by the ultrasonic cleaning
process using a chemical solution other than SC1. For example, the
wafers W may be cleaned by the ultrasonic cleaning process using a
pure water as a cleaning liquid. When the wafers W are cleaned by
the ultrasonic cleaning process using a pure water as a cleaning
liquid, the rinsing process can be omitted.
In the foregoing embodiment, the ultrasonic generator 30 is stopped
so as not to generate ultrasonic waves in the pure water (cleaning
liquid) during the rising process for rinsing off the chemical
solution (cleaning liquid) with a pure water (cleaning liquid).
However, not limited thereto, it is possible to generate ultrasonic
waves in the cleaning liquid (pure water) contained in the cleaning
tank 12 by means of the ultrasonic generator 30 during the rinsing
process for rinsing off the chemical solution (cleaning liquid), so
that a rinsing effect of the rinsing process can be enhanced and
particles (foreign matters) still remaining on the wafer W can be
further removed. In this case, it is possible to rinse relatively
uniformly the entire surfaces of the wafers W at relatively a high
rinsing efficiency, and to remove relatively uniformly particles
from the entire surfaces of the wafer W at relatively a high
removing efficiency, by supplying or not supplying the cleaning
liquid into the cleaning tank, or by changing a supply rate at
which the cleaning liquid is supplied into the cleaning tank, while
ultrasonic waves are generated in the cleaning liquid contained in
the cleaning tank 12.
Some possible modifications have been described with respect to the
above embodiment. Naturally, these modifications can be suitably
combined with each other.
The substrate cleaning system 10 has the control device 18
including the computer. The control device 18 controls operations
of the components of the substrate cleaning system 10 so as to
clean the wafer to be processed W. The present invention provides a
program to be executed by the computer of the control device 18 so
as to accomplish the wafer cleaning process, and the
computer-readable storage medium 19 storing this program. The
storage medium 19 may include a flexible disk, a hard disk, or the
like.
Although the substrate cleaning methods, the substrate cleaning
systems, the program, and the storage medium according to the
present invention have been described as applied to cleaning the
wafer W, the present invention is not limited thereto. For example,
the present invention is applicable to cleaning LCD substrates, CD
substrates, and the like.
EXAMPLES
In order to provide a more detailed explanation of the present
invention in terms of the examples, two experiments were
performed.
EXPERIMENT 1
After cleaning liquid was supplied into the cleaning tank, a test
wafer was immersed in the cleaning liquid contained in the cleaning
tank, and ultrasonic waves were generated in the cleaning liquid.
The experiment was performed under two conditions. Namely, in one
cleaning condition, ultrasonic waves were generated in the cleaning
liquid contained in the cleaning tank with the cleaning liquid
being continuously supplied (replenished) into the cleaning tank,
and in the other cleaning condition, ultrasonic waves were
generated in the cleaning liquid contained in the cleaning tank
with no cleaning liquid being supplied (replenished) into the
cleaning tank.
The cleaning liquid for use in this experiment contained nitrogen
and oxygen dissolved therein at the respective saturated
concentrations. The temperature of the cleaning liquid was
25.degree. C. Except for these parameters, general parameters for
an ultrasonic cleaning process for processing wafers were employed.
For example, a time period for generating ultrasonic waves was 10
minutes. 4,000 particles had been uniformly adhered in advance to
each test wafer used in this experiment. There was used in this
experiment a cleaning tank, as shown in FIGS. 1 and 2, which can
receive a plurality of wafers and is provided with cleaning nozzles
disposed on lower side parts of the tank for supplying cleaning
liquids.
Experiment results are shown in Table 1 and FIG. 7. Table 1 shows
particle removing efficiencies (=(the number of particles remaining
on the test wafer after the ultrasonic cleaning)/4,000.times.100
(%)) for a case in which the cleaning liquid was supplied
(replenished) into the cleaning tank during when ultrasonic waves
were generated in the cleaning liquid contained in the cleaning
tank, and for a case in which no cleaning liquid was supplied
(replenished) into the cleaning tank is suspended during when
ultrasonic waves were generated in the cleaning liquid contained in
the cleaning tank. After the ultrasonic cleaning process, where the
particles on the test wafers had been removed at a high removing
efficiency was observed. FIG. 7 shows the results. In FIG. 7, the
shaded portions depict areas which are observed that the particles
were removed at high removing efficiency. The arrangement of each
test wafer in the plane of FIG. 7 corresponds to the arrangement of
the test wafer in the cleaning tank. Namely, a lower part of the
test wafer in the plane of FIG. 7 was oriented downward in the
cleaning tank (near the vibrating members of the ultrasonic
generator) during the ultrasonic cleaning.
TABLE-US-00001 TABLE 1 Experiment Results of Experiment 1 Supply of
Cleaning Liquid during Ultrasonic Cleaning Supplied Not Supplied
Particle Removing Efficiency (%) 61.4 58.0
As understood from FIG. 7, in the case where the ultrasonic
cleaning was conducted with the cleaning liquid being replenished,
the lower area of the test wafer, i.e., the area near the vibrating
members of the ultrasonic generator, was cleaned at a high particle
removing efficiency. In the case where the ultrasonic cleaning was
conducted with the cleaning liquid being replenished, the area of
the test wafer positioned above the bar members of the holding
member had a degraded particle removing efficiency.
On the other hand, as understood from FIG. 7, in the case where the
ultrasonic cleaning was conducted with no cleaning liquid being
replenished, the upper area of the test wafer was cleaned at a high
particle removing efficiency.
EXPERIMENT 2
The following experiment was performed as an example of the present
invention. As shown in FIG. 3, a test wafer was subjected to the
ultrasonic cleaning process for 5 minutes, while the cleaning
liquid was being replenished. Following thereto, the test wafer was
subjected to the ultrasonic cleaning process for 5 minutes, while
the replenishment of the cleaning liquid was stopped for 5 minutes.
The rest parameters for the ultrasonic cleaning process were the
same as those in Experiment 1. Similar to Experiment 1, there was
used a test wafer to which 4,000 particles had been uniformly
adhered in advance.
The experiment result are shown in Table 2. Comparative Example 1
in Table 1 is a particle removing efficiency of Experiment 1 in
which the ultrasonic cleaning was conducted for 10 minutes with the
cleaning liquid being continuously replenished. Comparative Example
2 in Table 1 is a particle removing efficiency of Experiment 1 in
which the ultrasonic cleaning was conducted for 10 minutes with no
cleaning liquid being replenished.
TABLE-US-00002 TABLE 2 Experiment Result of Experiment 2
Comparative Comparative Example Example 1 Example 2 Supply of
Cleaning Liquid supplied .fwdarw. supplied not supplied during
Ultrasonic Cleaning not supplied Particle Removing 71.4 61.4 58.0
Efficiency (%)
As shown in Table 2, the wafer, which was subjected to the
ultrasonic cleaning process under the condition of Experiment 2,
was cleaned at the highest particle removing ratio. The surface of
the test wafer which had been cleaned under the condition of
Experiment 2 was observed, and it was found that the particles were
uniformly removed therefrom.
* * * * *